Hi guys, first post and newb so be nice.
I scored a 98 cbr600 f3, shed find, about 3 years ago for $1000 AUD and it had been sitting for a couple of years.
Long story short it came to life and has been running ever since with the odd hick up here and there like regulator/rectifier and fuel pump. All small things.
I change the fuel filter very regularly due to rust in the tank from those years of sitting. Since i bought it i always talked of new jets and seals etc due to it hating cold starts.
Not long ago i started to have a miss at high rpms under load which slowly turned into what felt like dropping a cylinder. Then one day it shut down completely.
I pulled the carbies out and chucked a kit through them with a good clean out.
Ran like a dream for three days and then started to have a miss again. Few km's down the road it then left me hanging on the side of the road waiting for a lift.
Chucked some new plugs in it and bang, started like nothing had happened. Again ran like a dream, loved cold starts and i then went for a good couple of hours ride without an issue. I parked it in the shed and the next day it wouldn't start.
I left it for a couple of days and came back to it to start straight away. I went for three quick short rides. Everything was fine until it shut down completely on the third. I got the bike home and parked it, went to work for a few hours and came home to it to start straight away. At this point i was extremely annoyed.
It then started sometimes to run fine. Then next start run rough. To then next start fine again to now it is only just turning over with no firing at all.
Ive replaced coils, plugs, cdi, pulse generator sensor, shorted pump to make sure its working, rebuilt carbs, checked fuel lines, air lines, earths, fuses, wiring loom looks fine, pulled fuel **** cleaned and made sure flow to carbs are fine.
What made me believe it might be a cdi issue was i had the carbies off and sprayed start ya bastard straight into the inlets. cylinder 2 and 3 would fire but 1 and 4 nothing. Swapped coil packs and still 2 and 3 would fire with nothing on 1 and 4.
I have spark at all plugs yet nothing will fire.
I am positive this has to be something small and stupid but i just cant for the life of me find it.
Any help or input would be greatly appreciated.
Ive tested the pulse generator with a tester and its within manual specs, same with the coil packs and leads.
WHAT AM I MISSING???
Very close to giving up and parting it out

 

I know it sounds daft but have got enough fuel in it

 

Yep, i have run out of fuel once while owning this bike and it will never happen again haha

 

could be **** got in to the jets from the tank as you run out off fuel

 

That has happened to me before.

 

Unfortunately not that simple. Ive had the carbs out a few times thinking i had done something wrong but nothing.
Its been a few years since i had let it run dry.

 

Ok i have had some progress.
I tested all components and everything was within specs and testing ok. So i decided to replace the plugs.....AGAIN.
Well it worked and she started. Idles fine, in neutral it revs fine. But mid range under load it misses big time. Around the 4000 to 5000rpm mark it starts and continues while giving it full throttle. If i ease through the throttle and slowly increase the speed it runs through the rev range with minimal miss if any.
Any ideas on where i should start looking?
Id like to believe its coil packs, but i have two sets here that test within specs so i don't like my chances. I have tried both with the same results.
I looked for leaks, both fuel and inlet, with nothing showing itself.
I believe my carbs are slightly out of sync with a tiny bit of fluctuation on idle, but i don't believe that would effect mid range rpm. Correct me if i am wrong.
I seen on another thread someone had similar issues mid range but they couldn't ease through on the throttle and it came down to ram air issues.
All my inlet hoses are plumbed where they are meant to be, the front pickup hose in the fairing is in tact and in position. The air flow relay tests ok, the solenoid tests ok, all lines are clear.
Ive gone through just about the whole workshop manual and tested all that i can with no success.
I've gone through as many threads as i can with similar issues and tried all everyone has done to theirs with no success.
Im nearly ready to sell it to someone to scrap i am that annoyed, even though i love the bloody thing.
Losing patience now. It has been a good few months of chasing problems with minimal success and neighbours now taking videos of me going up and down the road as they are annoyed LOL

 

I definitely would check the sync on the carbs. If they're off then you need to adjust your a/f mixture after the sync is complete.
also when troubleshooting carb issues, don't think RPMs. Think throttle position. Where you are in the throttle dictate what carb circuit is engaged. That will better help you when trying to trace things down. RPMs are a byproduct of everything else and not always accurate.

 

What has me stuffed is the bike has run with no issues with this set up for years without an issue. The carbs would only be out by the smallest amount if they are. Mid Range fueling issues would make me believe main jets are the issue but like i said the jets are 140 main jets on 2 and 3 and 138 on 1 and 4 and have been since well before i have got my hands on it.
The plugs are a soft dry black when i pull them out where the soot is easy to wipe off, but they all look the same. So hard for me to diagnose which carbs is the issue. Im no mechanic but i bought this bike knowing i would learn. So far i have learnt alot LOL.

 

Did you ever get this sorted? What exhaust/can do you have on there? 140 mains are quite large for stock. I run an a/f ratio gauge on mine and even with a k + n filter and aftermarket can it needs stock main jets or it is quite rich. I think the 4 into 2 into 1 on these is quite restrictive. I do have dynojet needles though which are quite short - if yours are longer they might need more main jet to deliver the same fuel up top.

Have you checked the air solenoid is opening above 12mph as it should? As these bikes have ram air systems, all that hosing **** running to the carbs is to balance the pressure to the float bowls and vacuum slides otherwise it wouldn't fuel right with the increased pressure from a pressurised airbox. If your solenoid doesn't open it might explain a bog.

All that said, it sounds like you could be lean on your pilots either because they're blocked or just not adjusted right - you need about 2 1/4 turns out (checked with a/f gauge) to give a 13.5:1 ish ratio at idle. If you're lean here you could find it misses as you roll on even at motorway speed. I had something similar before I was able to measure the fuelling properly - had the pilot too lean and at motorway speed if you rolled off to change gear or were at a low rev cruise it would feel as if you were running out of fuel. You often don't release just how much time you spend on the pilot jets.

hope that helps

regards

Dan